Priming the Motor Cortex With Anodal Transcranial Direct Current Stimulation Affects the Acute Inhibitory Corticospinal Responses to Strength Training

Frazer, Ashlyn, Howatson, Glyn, Ahtiainen, Juha, Avela, Janne, Rantalainen, Timo and Kidgell, Dawson (2019) Priming the Motor Cortex With Anodal Transcranial Direct Current Stimulation Affects the Acute Inhibitory Corticospinal Responses to Strength Training. Journal of Strength and Conditioning Research, 33 (2). pp. 307-317. ISSN 1064-8011

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Abstract

Synaptic plasticity in the motor cortex (M1) is associated with strength training and can be modified by transcranial direct current stimulation (tDCS). The M1 responses to strength training increase when anodal-tDCS is applied during training due to gating. An additional approach to improve the M1 responses to strength training, which has not been explored, is to use anodal-tDCS to prime the M1 before a bout of strength training. We examined the priming effects of anodal-tDCS of M1 on the acute corticospinal responses to strength training. In a randomized double-blinded cross-over design, changes in isometric strength, corticospinal-excitability and inhibition (assessed as area under the recruitment curve [AURC] using transcranial magnetic stimulation [TMS]) were analysed in 13 adults exposed to 20-min of anodal and sham-tDCS followed by a strength training session of the right elbow-flexors. We observed a significant decrease in isometric elbow-flexor strength immediately following training (11-12%; P < 0.05) which was not different between anodal-tDCS and sham-tDCS. TMS revealed a 24% increase in AURC for corticospinal-excitability following anodal-tDCS and strength training; this increase was not different between conditions. However, there was a 14% reduction in AURC for corticospinal inhibition when anodal-tDCS was applied prior to strength training when compared to sham-tDCS and strength training (all P < 0.05). Priming anodal-tDCS had a limited effect in facilitating corticospinal-excitability following an acute bout of strength training. nterestingly, the interaction of anodal-tDCS and strength training appears to affect the excitability of intracortical inhibitory circuits of the M1 via non-homeostatic mechanisms.

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